1. Field of the Invention
The present invention generally relates to magnetic sensing elements for use in hard disk devices or magnetic sensors. In particular, it relates to a magnetic sensing element having excellent resistance to electrostatic discharge damage and electrical overload, i.e., resistance to soft electrostatic discharge damage (ESD), when the size of the element is reduced, and to a method for making the magnetic sensing element.
2. Description of the Related Art
FIG. 24 is a cross-sectional view showing the structure of a conventional magnetic sensing element viewed from a face that opposes a recording medium.
The magnetic sensing element shown in FIG. 24 is a spin-valve magnetic element, which is a type of giant magnetoresistive (GMR) element, and detects a recording magnetic field from a recording medium such as a hard disk.
The magnetic sensing element is constituted from a lower shield layer 1, a lower gap layer 2, a first antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic material layer 5, a free magnetic layer 6, second antiferromagnetic layers 7, electrode layers 8, an insulating layer 9, an upper gap layer 10, and an upper shield layer 11.
Generally, the first antiferromagnetic layer 3 and the second antiferromagnetic layers 7 are composed of a Fe—Mn (iron-manganese) alloy, the pinned magnetic layer 4 and the free magnetic layer 6 are composed of a Ni—Fe (nickel-iron) alloy, the nonmagnetic material layer 5 is composed of copper (Cu), and the electrode layers 8 are composed of chromium (Cr). The lower shield layer 1 and the upper shield layer 11 are composed of a NiFe alloy and the lower gap layer 2, the insulating layer 9, and the upper gap layer 10 are composed of alumina.
The pinned magnetic layer 4 is magnetized and is put to a single domain state in the Y direction in the drawing by the exchange anisotropic magnetic field with the first antiferromagnetic layer 3. The Y direction is the direction of a leakage magnetic field from a recording medium and is the height direction.
The free magnetic layer 6 is put to a single magnetic domain state in the X direction by the exchange anisotropic magnetic field with the second antiferromagnetic layers 7. In other words, the free magnetic layer 6 is put to a single magnetic domain state in the X direction by exchange biasing. In exchange biasing, no dead zone, i.e., the zone that cannot detect magnetic fields, exists in the optical track width region; accordingly, the magnetic track width can readily coincide with the optical track width. Moreover, the demagnetizing field generated in the free magnetic layer 6 can be decreased.
In this magnetic sensing element, a detection current, i.e., a sensing current, is supplied from the electrode layers 8 to the free magnetic layer 6, the nonmagnetic material layer 5, and the pinned magnetic layer 4 via the second antiferromagnetic layers 7. Since a recording medium, such as a hard disk, moves in the Z direction and a leakage magnetic field from the recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer 6 shifts from the X direction toward the Y direction. The shift in the magnetization direction of the free magnetic layer 6 with respect to the magnetization direction of the pinned magnetic layer 4 changes the electrical resistance, thereby producing a magnetoresistive effect. Changes in electrical resistance result in voltage change, and the leakage magnetic field from the recording medium is detected based on the voltage change.
FIG. 25 is a plan view of the second antiferromagnetic layers 7 and the free magnetic layer 6 included in the magnetic sensing element of FIG. 24 viewed from the top of the drawing in FIG. 24, i.e., viewed in the direction opposite to the Z direction.
No investigation has been made on planar shapes of the second antiferromagnetic layers 7 and the free magnetic layer 6 of the spin valve magnetic sensing element of an exchange bias type. Particularly, the shapes and the dimensions of these layers at the portions inward from the opposing face in the Y direction have been out of the consideration.
Conventionally, as shown in FIG. 25, rear faces 7a of the second antiferromagnetic layers 7 and a rear face 6a of the free magnetic layer 6 have been formed as planes parallel to the X direction, i.e., the track width direction. Moreover, the distance between the opposing face and the rear faces 7a of the second antiferromagnetic layers 7 has been the same as the distance between the opposing face and the rear face 6a of the free magnetic layer 6, as indicated by reference character hl.
However, the magnetic sensing element including the second antiferromagnetic layers 7 and the free magnetic layer 6 arranged as above significantly suffers from a problem of ESD, in particular, soft ESD, when the size of the magnetic sensing element is reduced.
As the element becomes smaller, the second antiferromagnetic layers 7 that function as a path for power supply become smaller, resulting in an increase in the resistance. Thus, a large amount of heat is generated at the junctions between the free magnetic layer 6 and the second antiferromagnetic layers 7 when the magnetic sensing element comes into contact with an object with static charges or when a transient current flows during switching.
In the magnetic sensing element shown in FIG. 25, the transient current flows in the same direction as the sensing current, i.e., the X direction or a direction antiparallel to the X direction. Accordingly, the magnetic field generated by the transient current is in a direction perpendicular to the magnetization direction of the free magnetic layer 6.
Because of the heat and the generated magnetic field perpendicular to the magnetization direction of the free magnetic layer 6, the intensity and direction of the exchange anisotropic magnetic field between the free magnetic layer 6 and the second antiferromagnetic layers 7 are shifted. Although the magnetic sensing element does not break, the output symmetry is degraded, and output is decreased. Such phenomena are generically called soft electrostatic discharge damage (ESD).